Fuzzers and static checkers might not detect when mptcp_sk() is used
with a non mptcp_sock structure.

This is similar to the parent commit, where it is easy to use mptcp_sk()
with a TCP sock, e.g. with a subflow sk.

So a new simple check is done when CONFIG_DEBUG_NET is enabled.
mptcp_sk() is then used as an inlined function, like before commit
403a40f2304d ("mptcp: preserve const qualifier in mptcp_sk()").

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index eefd1397106d..c10c778cd773 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -348,7 +348,16 @@ static inline void msk_owned_by_me(const struct mptcp_sock *msk)
 	sock_owned_by_me((const struct sock *)msk);
 }
 
+#ifdef CONFIG_DEBUG_NET
+static inline struct mptcp_sock *mptcp_sk(const struct sock *sk)
+{
+	WARN_ON(sk->sk_protocol != IPPROTO_MPTCP);
+
+	return (struct mptcp_sock *)sk;
+}
+#else
 #define mptcp_sk(ptr) container_of_const(ptr, struct mptcp_sock, sk.icsk_inet.sk)
+#endif
 
 /* the msk socket don't use the backlog, also account for the bulk
  * free memory

-- 
2.43.0

Hi Matthieu,

Thank you for your modifications, that's great!

Our CI (GitHub Action) did some validations and here is its report:

- KVM Validation: normal:
  - Success! ✅:
  - Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/7728700216

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/399e99c4147f


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)

Hi Matthieu,

Thank you for your modifications, that's great!

Our CI (Cirrus) did some validations with a debug kernel and here is its report:

- {"code":404,"message":
  - "Can't find artifacts containing file conclusion.txt"}:
  - Task: https://cirrus-ci.com/task/4603007531220992
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/4603007531220992/summary/summary.txt

- {"code":404,"message":
  - "Can't find artifacts containing file conclusion.txt"}:
  - Task: https://cirrus-ci.com/task/5728907438063616
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/5728907438063616/summary/summary.txt

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/399e99c4147f


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-debug

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)